Introduction
1. Ugrasena was the father of Kansa and Devki(mother of Krishna), and was the King of Mathura.
2. Ugrasena was imprisoned by his own son Kansa.
3. After Lord Krishna killed Kansa, Ugrasena was reinstated as King.
Vasudeva Gave Mathura to Ugrasena
1. Ugrasena didn’t become the king of Mathura by right.
2. Mathura was ruled by Shurasena.
3. Shurasena’s son was Vasudeva, Krishna’s father, who gave up the right to the kingdom and began raising cows with his cousine Nand.
4. Because of that, Ugrasena, another Yadava king had to rule Mathura as per Devibhagavata Chaturthaskanda.
Kansa & Ugrasena
1. Kamsa is believed to be Ugrasena’s son, but he was born to Ugrasena’s wife and a gandharva named Dramila.
2. Once , in her youth, Ugrasena’s wife was walking in the forests with her maids when Dramila saw her and impregnated her.
3. She was furious and said that since Dramila had made her pregnant using devious means, a child born of her husband’s clan would kill Dramila’s child.
4. Kamsa imprisoned Ugrasena and as per his mother’s words, he died at the hands of Krishna, who belonged to Ugrasena’s clan.
5. Narada had informed Kamsa about these words, and Kamsa mentioned it to Akrura when he sent Akrura to fetch Krishna for the Dhanuryaga as per Bhagavata Dashamaskanda.
6. Though Ugrasena is believed to be the son of Aahuka, some scriptures maintain that Ugrasena was also known as Aahuka – Mahabharata Udyogaparva Chapter 128 verse 39.
7. Lord Krishna later killed Kansa and Freed Ugrasena and made him king of Mathura.
8. During Ugrasena's reign, Mathura was attacked by Jarasandha(Father in law of Kansa) and Shalva.